Electrical apparatus



June 2, 1931.

ELECTRICAL o. E. MARVEL APPARATUS Filed March 30, 1925 w W s mi.

Patented June 2, 1931 UNITED STATES PTENT OFFICE ORIN E. MARVEL,OF'DAYTON, OHIO, ASSIGNOR', BY MESNE ASSIGNMENTS, TO GENERAL MOTORSRADIO CORPORATION, OF DAYTON, OHIO, A CORPORATION OF OHIO ELECTRICALAPPARATUS Application filed March 30, 1925.

The present invention relates to electrical apparatus having to do withthe control of electrical circuits and particularly with the control ofradio circuits. 7 7

One of the principal objects of the invention is to provide means forconcurrently varying the selectivity or decrement of one or more groupsof coupled circuits.

' Still a further object is to provide means for eliminating or reducingthe efiects of undesirable or stray waves, such as atmosphericdisturbances or shocks, upon electrical apparatus.

Further objects of the invention will be apparent from the followingdescription when taken in connection with the accompanying drawings, inwhich Fig. 1 is a diagrammatic view of a receiving apparatus embodyingthe present inven tion; and

Fig. 2 is a detail view illustrating certain features of construction ofFig. 1.

While the present invention is capable of embodiment in numerous-forms,there is illustrated herein a preferred embodiment of the same, in which20, 21 and 22 designate vacuum tubes or electron discharge devices ofthe audion type, each havinga heated electron discharge cathode orfilament 23, a grid or input terminal 2d and a plate or output terminal25. The electron discharge devices or tubes 20 and 21 are hereinemployed for amplifying the electrical oscillations received thereby,and the electron discharge device or tube 22 is employed as a detectorfor translating radio frequency energy oscillations or signals intoaudio frequency energy oscillations or signals. It is not at allessential that the detector should be of the vacuum tube type, assatisfactory results may be obtained with a crystal or other type ofdetector. 7

Heating current for the filaments 23 is supplied from the source ofcurrent 26 through suitable conductors 27 and 28, and each filament maybe provided with a resistance 29 to regulate the flow of currenttherethrough. The conductor 27 connected with the nega-j tive side ofthe battery or source of current 26 has been indicated by a heavy lineand may be termed the common or negative side Serial No. 19,369.

energy transmitting relationship with the input circuit of the tube 21,and the output circuit of, the latter is likewise in energy transmittingrelationship with the input circuit of the tube 22, so that the tubes20, 21 and 22 are thus said to be connected in cascade. Electricallyconnected with input circuit of the first vacuum tube 20 is a receivingor antenna circuit 30 which may be provided with the usual antenna andgrotmd connections.

The antenna or receiving circuit 30 is connected with the input circuitof the first tube 20 and the output circuit of each tube is connectedwith the input circuit of the next succeeding tube through the mediumoftransformers 31, 32 and 33 which will now be described. The primarywinding of each transformer is herein illustrated as comprising a pairof coaxial coils 34 and 35 which coils are spaced apart and innon-inductive relationship with one another, that is, they are wound sothat their electrical effects are in opposition to one another. Thecoils 34 and 35 of the primary arepreferably wound upon acontrol tube 36as shown in Fig. 2. WVound upon a suitable tube or frame 37 surroundingthe tube 36 is a secondary winding 38 which is disposed intermediate thecoils 3d and 35 of the cooperating primary winding. Coils 34 and 35 ofthe primary winding are preferably of an equal number of turns and eachhave an inductive effect upon the secondary winding 38 but in oppositedirections. The control tube 36 carrying the coils 34L and 35 of theprimary winding is preferably mounted for longitudinal axial movementwhereby the coils 34 and 35 may be moved simultaneously within thesecondary winding 38, and in this manner the relative inductive efiectsof thecoils 34 and 35 upon the secondary wind ing 38 may be varied toany desired extent, For example; when the tube 36 is moved to the rightso that the coil 34 is opposite the secondary winding 38 then there is amaximum degree of coupling of the primary and secondary windings in onedirection, and likewise when the coil 35 is moved opposite the winding38 then there is a maximum degree of coupling in the opposite direction.Various degrees of coupling between the maximum in one direction and themaximum in the other direction may be obtained by causing the secondarywinding to assume various positions between the coils 34 and 35, andwhen the inductive effect of these coils upon the secondary winding 38is nearly equal or balanced then the coupling is of nearly zero value sothat there is almost no transfer of energy from the primary to thesecondary winding. At this time the transformer may be said to possessits greatest selectivity or in other words its minimum 'decrement.

The construction and arrangement of the primary and secondary windingsof the transformers 32 and 33 are substantially the same as that of thetransformer 31. However the several transformers are so interconnectedthat the variation in coupling of the several transformers may beaccomplished simultaneously or concurrently, and also equally ifdesired. This may be accomplished by mounting all the primary windingsupon a single control tube 36, as illustrated, whereby the primarywindings may be moved simultaneously relative to the secondary windings,or this may be accomplished in any other convenient manner.

In the circuit arrangement illustrated in Fig. 1 each of the secondarywindings 38 is connected in the. grid or input circuit of a vacuum tubeor electron discharge device, said input circuit extending from the grid24 through the secondary winding 38 to the common or negative conductor27. The input circuits are preferably provided with adjustablecondensers 39 whereby the several input circuits may be tuned to thesame frequency. The primary windings of the transformers 32 and 33 areconnected in the output circuits of the tubes 20 and 21 the circuitsextending from the plate terminals 25 through fixed condensers 41, coils34 and 35' of the primary, and thence to the negative conductor 27.Suitable plate voltage is impressed upon the output circuits of thetubes 20 and 21 by means of the conductors 42 connected with thepositive terminal of battery 264344, the conductors 42 being providedwith suitable choke coils 45 which offer a high impedance to the radioor high frequency current, and thereby cause the same to flow throughthe primary windings of the transformer instead of passing off throughthe conductors 42. The output circuit of the detector tube 22 extendsfrom the plate terminal 25 through a telephone or translating device 46to the positive side of the battery 2643. v

The operation of the present invention may be explained by reference toFig. 1. As-

suming that the secondary winding 38 is in the mechanically midway orcentral position between the primary windings 34 and 35, and furtherthat high frequency currents of a given frequency and of continuous andsustained character are being impressed upon the primary circuit, itwill be seen that the fiow of this high frequency current in the firstcoil 34 of the primary winding acts inductively upon the nearest part ofthe secondary winding 38 to induce a current therein, as indicated bythe arrow 50. This induced current may be assumed to travel from left toright through the secondary winding towards the grid 24 in order toimpress its effect upon the grid, but owing to the length of thesecondary winding a certain length of time is consumed in moving throughthe winding 38. The impressed hi h frequency currents after they leavethe first primary winding 34, pass to the second primary winding 35causing the latter to act upon the nearest or right hand end of thesecondary winding 38, as indicated by thearrow 51, to induce a currenttherein which is in opposition to the current induced by the primarywinding 34.

However, owing to the fact that the current induced in the secondarywinding by the first primary coil 34 must pass through the length of thesecondary 38 and is necessarily retarded somewhat by the impedance ofthis winding, the current induced in the secondary winding by the coil35 predominates for the time being and the effect thereof is impressedupon the grid 24. To establish an electrical balance between thecurrents induced in the secondary winding by the coils 34 and 35, theprimary windings may be moved to the right, out of the mechanicallycentral position, so as to increase the inductive effect of coil 34 anddecrease the effect of coil 35 upon secondary winding 38. In this manneran adjustment maybe made such that the current flowing through the twoprimary coilsv 34 and 35 has no effect upon the grid'24, and the primaryand secondary windings of the transformer are then said to be in neutralor zero coupling position. In the above dis cussion it has beenassumed'that the current impressed upon the primary winding is of agiven frequency and wave character, as for example, the current that isreceived from a broadcasting station which is generally of a continuousand sustained character. The current received from such a station hasmore or less uniform characteristics, that is, thewave form, thepotential, and other factors are of a uniform nature. Such waves whenimpressed upon the primary winding of the present invention induceenergy oscillations or currents in the secondary winding, but owing tothe impedance of the secondarycircuit and other-electrical factors, thephase relations of the current and voltage induced in the secondarywinding are altered, that is to say, the power factor of the inducedcurrent is not the same as the power factor of the current impressedupon the primary winding.

Should high frequency currents of other characteristics than the currentabove referred to be impressed upon the primary winding, as for examplecurrents having other frequencies, or irregular frequencies or irregularwave forms as in the case of atmospheric disturbances, then theimpedance of the secondary winding with respect to these latter currentsis not the same as it is for the currents of given frequency andcharacteristics as first referred to, and the secondary winding willtherefore have different zero or neutral coupling positions for currentsof different characteristics. In operation the primary and secondarywindings are so adjusted as to assume zero or neutral coupling positionfor the undesirable or socalled disturbing electrical currents, as forexample, the atmospheric disturbances. In this position the windings arenot in neutral or zero coupling position with respect to the electricaloscillations or currents of desirable characteristics and the latter aretherefore impressed upon the grid 24.

From the foregoing it will be apparent that energy oscillations orcurrents of different characteristics impressed upon the primary windingare affected unequally in transmission to the secondary winding, andconsequently one may adjust the apparatus so as to eliminate or suppressthe effect of the currents of undesirable or disturbing characteristicsupon the grid circuit. Stated in other words, the apparatus hereindescribed may be said to function as a selector for selecting the wavesof the desired characteristics and, comparatively speaking, suppressingthe effect of the waves of undesirable characteristics to an extentdepending upon the adjustment of the apparatus. Although waves ofvarious frequencies and characteristics are picked up by the antennacircuit 30 and imressed upon the transformer 31, the windings of thelatter may be so adjusted that waves having the desired characteristicshave a maximum effect upon the grid of vacuum tube 20 whereas the effectof waves of different and undesirable characteristics is suppressed tosay, for example one-half of their original value. Energy waves oroscillations impressed upon the grid and input circuit of the firstvacuum tube 20 are amplified in a manner well understood in the art andsuch amplified waves are impressed upon the primary circuit oftransformer 32. Assuming that here also the waves of undesirablecharacteristics are suppressed to one-half their value, as compared withthe waves of the desired characteristics, it will be seen that theeffect of the former upon the grid of vacuum tube 21 hasbeen reduced toonefourth the effect of the latter. 'wise the disturbing waves ofundesirable And likecharacteristics are also suppressed by thetransformer 33 so that their effect upon the grid of detector tube 22 isnow but one-eighth.

of their original value as compared with the I do not wish to .belimited thereby as the in.-

vention is in no way dependent upon an accurate understanding of thetheory and shouldnot be construed as limited by such considerations.-

While the invention has been herein jde- I scribed and illustrated inits application to a receiving apparatus for amplifying and detectingradio. frequency currents, it should be understood that it isnot'liinited to this precise application but is equally useful in,apparatus employing low frequency transformers as, for example, in theamplification of audio frequency currents. Also it should be understoodthat the invention is not limited to the precise arrangement of coaxialprimary and secondary windings herein described nor need the separatecoils of the primary winding have an equal number of turns, since anyconstruction and arrangement of the parts capable of producing theresults herein described is considered as coming within the scope of thepresent invention.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus,. and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. In an apparatus of the character de-' scribed, several pairs ofcoupled circuits connected for concurrent operation in cascade,

and means for concurrently varying thecoupling relation of said pairs ofcircuits, each of said pairs of coupled circuits having inductivelycoupled primary and secondary windings, and said means having a singlemovable member to which a winding of each pair is securely fixed forbodily varying in unison the relative positions of the primary andsecondary windings of said pairs.

2. In an apparatus of the character described, several pairs of coupledcircuits connected for concurrent operation in cascade, one of saidpairs of circuits comprising a grid circuit having a secondary windingtherein and a grid connected with one end of said secondary winding, aprimary circuit having a primary winding therein said primary windingcomprising opposed relatively fixed coils each adapted to be inductivelycoupled with said secondary winding, and means for concurrently changingthe coupling relation of said pairs of circuits to cause atthe grid endof said secondary winding an appreciable time lag between voltageinduced in the secondary winding by one of said coils and the voltageinduced in said secondary winding by the other of said coils.

3. In an apparatus of the character described, a pair of couplingcircuits, and means for varying the coupling relation of said circuitscomprising coupled primary and secondary windings in said circuits, oneof said windings having spaced relatively fixed coaxial coils wound inseries to produce opposed inductive effects, and *the other windingcomprising a coil inductively associated with both said coaxial coils,and means for relatively moving said primary and secondary windingscoaxially.

In testimony whereof I hereto aflix my signature.

ORIN E. MARVEL.

